This invention relates to a stent delivery system. More particularly, this invention relates to a balloon sheath for sheathless delivery of balloon-expandable stents.
The concept of implantable stents for use in medical applications has been known for many years, and a primary means of delivering an unexpanded stent into a body vessel or cavity is by use of a balloon catheter. In practice, the stent is mounted at the distal end of the catheter over an inflatable membrane (balloon) and is carried to a remote treatment area by guiding the catheter through appropriate corporeal vessels. Positioning of the catheter is tracked by fluoroscopic, radiographic or other suitable means, and, once the stent is properly positioned in a vessel or organ, the balloon is inflated, thereby forcing the stent outwardly into a fully expanded position.
Balloon-expandable stents have become a mainstay of vascular and non-vascular interventional procedures. All designs of balloon-expandable stents require mounting of the stent on a balloon, and some involve placement of a sheath over the balloon. Thus, balloon expandable stent delivery systems come in either sheathed or sheathless designs. FIGS. 1 and 2 illustrate a common prior art sheathless balloon-expandable stent delivery system in its undeployed and deployed states, respectively.
The sheath used in balloon-expandable stent delivery systems provides protection for the stent, prevents it from being dislodged from the balloon catheter, and also provides a smooth surface for reduction of friction between the stent and corporeal vessels. The sheath, however, increases the bulk and diameter of the stent delivery system and decreases its flexibility and trackability.
Sheathless stent delivery systems, on the other hand, have lower profiles and are more trackable. However, there is substantial friction between the irregular stent surface and corporeal vessel walls, particularly in areas of calcification. The uncovered stent may thus become damaged during placement due to contact with the guide catheter or corporeal vessel walls. The stent may also become dislodged from the balloon catheter, resulting in significant patient complications. In addition, the friction between the stent and corporeal vessel walls may cause damage to the vessel walls.
It is desirable to provide a delivery system that possesses the low profile and trackability of a sheathless system as well as the protection and decreased friction of a sheathed system.
It is, therefore, an object of the present invention to improved devices for implanting balloon-expandable stents.
It is another object of the present invention to enable more accurate positioning of a balloon-expandable stent during the implantation procedure.
It is a further object of the present invention to prevent the loss of a balloon-expandable stent from the insertion catheter during the implantation procedure.
It is yet another object of the present invention to provide a smooth surface for reduction of friction between a sheathless balloon-expandable stent delivery system and corporeal vessel walls.
It is yet another object of the present invention to increase the flexibility and trackability of a sheathless balloon-expandable stent delivery system.
These and other objects of the invention will become more apparent from the discussion below.
In accordance with these and other objects of the present invention, a sheathless balloon-expandable stent delivery system is provided. The ends of the balloon of the stent delivery system are invaginated and folded over onto the balloon itself such that, when a stent is mounted on the balloon, the balloon ends fold over the ends of the stent, thus covering the ends of the stent and protecting the stent and stent ends in the same manner that a sheath would. Dependent upon the length of the stent and the size and design of the balloon, the folded-over ends could cover the terminal portions of the stent or could reach to the middle of the stent and cover virtually the entire stent. When the balloon is inflated to deploy the stent, the balloon ends move substantially longitudinally as they inflate and uncover the stent.
Balloon inflation ports in the balloon catheter could optionally be positioned or configured to preferentially direct the inflation fluid into the balloon ends/invaginations to assure their inflation before the inflation of the body of the balloon. Because the stent will be in a crimped or undeployed state positioned circumferentially around the middle portion of the balloon, the pressure and radial force required to inflate the body of the balloon will be much greater than the pressure or force required to inflate the unrestricted balloon ends. The balloon ends will thus expand and move substantially longitudinally away from the ends of the stent before the stent expands so as not to become trapped between the stent and an organ or corporeal vessel wall.